1. Field of the Invention
The present invention relates to a method of manufacturing silicon semiconductor acceleration sensor devices and, more particularly, to a method of manufacturing built-in cantilever type silicon semiconductor acceleration sensor devices.
2. Description of the Related Art
Semiconductor acceleration sensors are designed to apply accelerative forces to, for example, a silicon thin plate by some means and to detect the deflection of the silicon thin plate caused by the application of the accelerative forces thereto in the form of changes in resistance of a gage resistor formed in a silicon thin plate. Conventional semiconductor acceleration sensors of the above-described type include a cantilever type semiconductor acceleration sensor such as that shown in FIGS. 4 and 5.
In this semiconductor acceleration sensor, accelerative forces are generated by the mass of an overall cantilever 1. Consequently, the vicinity of a supporting portion 2 of the cantilever 1 is subjected to a torque, causing the resistance of a gage resistor 3 embedded in the supporting portion 2 to change. These changes in the resistance are detected as a current or voltage change signal.
The conventional silicon semiconductor acceleration sensor arranged in the above-described manner is manufactured by the following procedures.
First, a silicon single crystal wafer 4 having a (100) orientation is oxidized to form an oxide film. Next, the oxide film formed around a portion which is turned into the cantilever 1 is removed in a U-shaped form using a photolithographic technique to form a U-shaped portion 5.
Thereafter, etching of the silicon is conducted using the oxide film 6 as an etching mask. The depth of an etched groove 7 generally ranges from 10 .mu.m to 80 .mu.m. After oxidation is conducted again, a P.sup.+ diffusion layer 8 is formed in the vicinity of the supporting portion 2 on which etching has not been conducted for the provision of an aluminum contact. Subsequently, four gage resistors 3 are formed in a bridge by the ion implantation.
Finally, aluminum wires 10 are led from a contact portion 9 of the gage resistors 3 for preparing the wiring for a power source and an output. At the same time, a bonding pad 11 is formed on the periphery of the acceleration sensor chip for wire bonding. Thereafter, a passivating nitride or oxide film 12 is applied to protect the aluminum wiring, and then the portion which is to be the cantilever 1 is thinned from the rear surface of the acceleration sensor chip by alkali anisotropic etching. As shown in FIG. 6, an etched surface 13 gradually proceeds and finally reaches the etched groove 7 formed in the U-shaped portion 5. At this time, etching is suspended whereby the cantilever 1 is formed. The built-in cantilever type acceleration sensor wafer formed in the manner described above is diced into individual chips in such a manner that the cantilevers 1 do not break to produce semiconductor acceleration sensor chips.
In the above-described silicon semiconductor acceleration sensor manufacturing method, a wafer 4 on which the cantilevers 1 have been formed must be handled very carefully. Or, the cantilevers 1 may be damaged and do not function. The cantilevers 1 which remain unbroken until after dicing may be broken in the subsequent assembly process. The rate of the cantilevers 1 which remain unbroken until after characterizing tests are finished is very low. The built-in cantilever type acceleration sensor is therefore very expensive although it is small in size.